Since the new generation of microwave links and mobile relays operates in the 22 GHz range, it is becoming more and more necessary to use high stability sources having low power consumption and low cost. One means used for this purpose consists in using an oscillator including a solid-state component such as gallium arsenide field effect transistor (GaAs FET) stabilized by a dielectric resonator.
An oscillator of this type is described in U.S. Pat. No. 4,357,582. This patent describes a microwave oscillator comprising a field effect transistor disposed on a plane substrate. A first transmission line disposed on the substrate is connected to the gate of the transistor and is terminated by a matching impedance. A second transmission line is connected to the drain of the transistor and is disposed on the substrate at a predetermined angle relative to the first transmission line, with a third transmission line connected to the source of the transistor and disposed on the substrate in order to constitute an oscillation output. A dielectric resonator is disposed in the angle between the first and second transmission lines.
In said patent, the means used for adjusting the frequency of the oscillator consists in displacing a disk immediately over the dielectric resonator.
This highly practical means nevertheless suffers from the drawback of disturbing the field lines around the dielectric resonator. This gives rise to a reduction in Q factor.
The Q factor may vary between 1000, and 500 depending on the position of the disk over the dielectric resonator. This also gives rise to a reduction in frequency stability and in spectrum purity.
The object of the invention is to mitigate these drawbacks.